In this work we present a nonparametric approach, which works on minimal assumptions, to reconstruct the cosmic expansion of the Universe. We propose to combine a locally weighted scatterplot smoothing method and a simulation-extrapolation method. The first one (Loess) is a nonparametric approach that allows to obtain smoothed curves with no prior knowledge of the functional relationship between variables nor of the cosmological quantities. The second one (Simex ) takes into account the effect of measurement errors on a variable via a simulation process. For the reconstructions we use as raw data the Union2.1 Type Ia Supernovae compilation, as well as recent Hubble parameter measurements. This work aims to illustrate the approach, which turns out to be a self-sufficient technique in the sense we do not have to choose anything by hand. We examine the details of the method, among them the amount of observational data needed to perform the locally weighted fit which will define the robustness of our reconstruction. In view of our results, we believe that our proposal offers a promising alternative for reconstructing global trends of cosmological data when there is little intuition on the relationship between the variables and we also think it even presents good prospects to generate reliable mock data points where the original sample is poor.
We present a sample of 74 Gamma-Ray Bursts (GRBs) from the Fermi-GBM catalogue for which we compute the distance moduli and use them to constrain effective dark energy models. To overcome the circularity problem affecting GRBs as distance indicators, we calibrate the Amati relation of our sample with a cosmology-independent technique. Specifically, we use the latest observational Hubble parameter data, including associated systematics, to approximate the cosmic expansion through a Bezier parametric curve. We subsequently obtain the distance moduli of the GRBs and include the data in a suite of recent cosmological observations of the expansion history (Planck Compressed 2018, 2012 BOSS release of BAO data and Pantheon SNIa), to compute Bayesian posterior constraints for the standard cosmological model ΛCDM, as well as ωCDM, and the CPL parametrization. Throughout the analysis we strive to keep under control the error propagation and limit our GRBs sample to avoid observational bias. As a result, we find no evidence in favour of the alternatives to ΛCDM model. The latter agrees very well with our calibrated sample of GRBs and presently available luminosity distance probes.
Reaction of the thiaplatinacyle [(Et3P)2Pt(C12H8S-C,S)] (3; derived from reaction of [Pt(Et3P)3] and dibenzothiophene (DBT)) with HCl gives largely 2-phenylthiophenol and a small amount of DBT. The thiaplatinacycle [(Et3P)2Pt(C8H6S-C,S)] (2; from benzothiophene (BT)) undergoes reaction with HCl to give 2,3-dihydrobenzothiophene (22%), a small amount of 2-vinylthiophenol, and BT, while the thiaplatinacycle [(Et3P)2Pt(C4H4S-C,S)] (1; from thiophene) regenerates thiophene with HCl; in each case the metal is found as [(Et3P)2PtCl2]. In contrast all the thiaplatinacycles react very similarly with HBF4 to give dinuclear [Pt2(Et3P)4(μ-SR)2](BF4)2 (7c, R = 2-phenylthiophenolate (from 3); 7b, R = 2-vinylthiophenolate (from 2); 7a, R = 1-thiolatobutadiene (from 1)). An X-ray structure determination of 7c confirmed the structure. Reaction of the dications 7a − c with HCl gave C4H6S (59%), 2-vinylthiophenol (83%), and 2-phenylthiophenol (91%), respectively.
In this work we set observational constraints of the Superfluid Chaplygin gas model, which gives a unified description of the dark sector of the Universe as a Bose-Einstein condensate (BEC) that behaves as dark energy (DE) while it is in the ground state and as dark matter (DM) when it is in the excited state. We first show and perform the various steps leading to a form of the equations suitable for the observational tests to be carried out. Then, by using a Markov Chain Monte Carlo (MCMC) code, we constrain the model with a sample of cosmology-independent long gamma-ray bursts (LGRBs) calibrated using their Type I Fundamental Plane, as well as the Union2.1 set and observational Hubble parameter data. In this analysis, using our cosmological constraints, we sketch the effective equation of state parameter and deceleration parameter, and we also obtain the redshift of the transition from deceleration to acceleration: zt.PACS numbers: 98.80.Jk, 95.36.+x, 95.35.+d
In this paper we extend the range of consistency of a constant bulk viscosity model to redshifts up to z ∼ 8.1. In this model the dark sector of the cosmic substratum is a viscous fluid with pressure p = −ζθ, where θ is the fluid-expansion scalar and ζ is the coefficient of bulk viscosity. Using the sample of 59 high-redshift GRBs reported by Wei (2010), we calibrate GRBs at low redshifts with the Union 2 sample of SNe Ia, avoiding then the circularity problem. Testing the constant bulk viscosity model with GRBs we found the best fit for the viscosity parameterζ in the range 0 <ζ < 3, being so consistent with previous probes; we also determined the deceleration parameter q0 and the redshift of transition to accelerated expansion. Besides we present an updated analysis of the model with CMB5-year data and CMB7-year data, as well as with the baryon acoustic peak BAO. From the statistics with CMB it turns out that the model does not describe in a feasible way the far far epoch of recombination of the universe, but is in very good concordance for epochs as far as z ∼ 8.1 till present.
The luminosity distance describing the effect of local inhomogeneities in the propagation of light proposed by Zeldovich-Kantowski-Dyer-Roeder (ZKDR) is tested with two probes for two distinct ranges of redshifts: supernovae Ia (SNe Ia) in 0.015 ≤ z ≤ 1.414 and gamma-ray bursts (GRBs) in 1.547 ≤ z ≤ 3.57. Our analysis is performed by a Markov Chain Monte Carlo (MCMC) code that allows us to constrain the matter density parameter Ωm as well as the smoothness parameter α that measures the inhomogeneous-homogeneous rate of the cosmic fluid in a flat ΛCDM model. The obtained best fits are (Ωm = 0.285 −0.171 ) with a χ 2 red = 0.975. The value of the smoothness parameter α indicates a clumped universe however it does not have an impact on the amount of dark energy (cosmological constant) needed to fit observations. This result may be an indication that the Dyer-Roeder approximation does not describe in a precise form the effects of clumpiness in the expansion of the universe.PACS numbers: 98.80.Jk, 95.36.+x, 95.35.+d
We present a non-parametric reconstruction of the rotation curves (RC) for 88 spiral galaxies under the LOESS+SIMEX technique. In order to compare methods we also perform the parametric approach assuming core and cuspy dark matter (DM) profiles: PISO, NFW, Burkert, Spano, the soliton and two fuzzy soliton+NFW. As result of this two approaches, a comparison of the RC obtained is carried out by computing the distance between central curves and the distance between 1σ error bands. Furthermore, we perform a model selection according to two statistical criteria, the BIC and the value of χ 2 r ed . We work with two groups. The first one is a comparison between PISO, NFW, Spano and Burkert showing that Spano is the most favored model satisfying our selection criteria. For the second group we select soliton, NFW and Fuzzy models, resulting the soliton as the best model. Moreover according to the statistical tools and non-parametric reconstruction we are able to classify galaxies as core or cusp. Finally, using an MCMC method, we compute for each of the DM models the characteristic surface density, µ D M = ρ s r s , and the mass within 300 pc. We found that there is a common mass for spiral galaxies of the order of 10 7 M , which is in agreement with results for dSph Milky Way satellites, independent of the model. This result is also consistent with our finding that there is a constant characteristic volume density of haloes. Finally, we also find that µ D M is not constant, which is in tension with previous literature.
In previous papers, a cosmological model with constant-rate particle creation and vacuum term decaying linearly with the Hubble parameter was shown to lead to a good concordance when tested against precise observations: the position of the first peak in the spectrum of anisotropies of the cosmic microwave background (CMB), the Hubble diagram for supernovas of type Ia (SNe Ia), the distribution of large-scale structures (LSS) and the distance to the baryonic acoustic oscillations (BAO). That model has the same number of parameters as the spatially flat standard model and seems to alleviate some observational/theoretical tensions appearing in the later. In this letter we complement those tests with 109 gamma ray bursters (GRB), 59 of them with redshifts above z = 1.4, which permits to extend the Hubble diagram to redshifts up to z ≈ 8. For the calibration of the 50 GRBs with z < 1.4 we use the 288 supernovas of the Sloan Digital Sky Survey (SDSS) project, calibrated with the MLCS2k2 fitter, less model-dependent than other samples like Union2. Our results show a good concordance with the previous tests and, again, less tensions between SNe Ia and GRB best fits as compared to the standard model.
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